1. Field of the Invention
The present invention relates to apparatus which controls processes that supply a chemical substance to a particular location. In particular, it relates to a process that supplies a chemical substance such that the concentration of the chemical substance affecting the location is controlled at each and every point in time and is known at each and every point in time and where the parameters of various amplitudes, durations, rate dynamics, periodicities, frequency of oscillations, notch, plateau, bimodal, and phase relationships of the chemical substance can be controlled and manipulated with respect to time.
2. Description of the Prior Art
The maintenance of biological tissue, such as organs, isolated from their natural nutrient supply is of great importance. A significant amount of research has been done with regard to organs that have been removed from a body. The research is quite varied and ranges from simply trying to keep the particular organ alive outside of the body to studying the complex responses of the isolated organ to various chemical stimuli.
Typically, the organ is placed in a chamber and its biological function supported by some type of culture medium. Initially, the system used to keep an organ alive was a static one wherein the nutrients were initially mixed in the culture medium and were never replenished. This type of system was limited in its ability to sustain an organ in a biologically alive state since the culture medium very quickly became contaminated from the organ's waste products and natural secretions.
Deficiencies of the static system led to the development of a dynamic system wherein the culture medium and the chamber holding the organ was replenished and was capable of sustaining biological life for a significantly extended period of time. These systems are commonly referred to as perfusion, perifusion or superfusion systems and have significantly increased the time available for studying organs and other tissue outside of the body.
The perifusion system is a system wherein the organ is surrounded by a culture medium containing nutrients that are absorbed by the organ. The perfusion system supplies nutrients to the organ through the organ's cardiovascular system. The superfusion system includes a system that both perfuses and perifuses nutrients to the organ.
Typically, the dynamic systems include a chamber in which the organ or other tissue is placed. The chamber has an inlet for providing nutrient-containing culture medium and an outlet for removing culture medium at a rate which preferably keeps the volume of the culture medium constant within the chamber. The dynamic systems have several advantages. First, conditions in the dynamic systems more closely resemble conditions within the body than the conditions in a static system through the continuous turnover of the medium thereby minimizing the effect of secretion and waste product accumulation. Second, the organ can be presented to different reagents without removal of the organ from the chamber. Third, the effects of nutrients and other chemical stimuli may be studied by collecting samples from the outlet of the chamber and analyzing such samples.
However, the perfusion, perifusion and superfusion systems of the prior art have several limitations. First, only a static concentration of a chemical stimuli can be supplied to the organ such that the concentration is known at every point in time. Varying the concentration dynamically by providing "pulses" of chemical stimuli results in unknown concentrations with respect to time of the chemical stimuli affecting the organ in the culture chamber. Consequently, research to determine the response of an organ to various concentrations of chemical stimuli using a dynamic system has been often times ineffective.
Second, since only a static or pulsed concentration of a nutrient or other chemical stimuli can be presented to the organ, overdose or underdose has been a frequent result. In trying to sustain organs in a biologically alive state, the supply of the proper concentration of nutrients to the organ as the organ's need for nutrients changes with respect to time is extremely important in extending the biological life of the organ or in attempting to analyze the response of an organ to a chemical stimuli in a dynamic situation.
Some prior art processes which increase the concentration of a drug or stimuli being presented to a biological tissue increase the concentration in a pulse-type manner. The pulse-type process is a flow through system where a constant concentration "x" of the drug or stimuli is continually delivered to the tissue in a supportive media. To increase the concentration affecting the tissue, a specific volume of a concentration "y" of the drug or stimuli greater than concentration "x" is injected into a holding chamber which houses the tissue. At the time of injection, if the volume in the holding chamber is known and the volume of supportive medium containing concentration "y" injected is known, then the initial concentration at the time of injection will also be known. However at any time after injection, the concentration will decrease as the supportive media containing concentration "x" continues to flow through. Thus, the concentration affecting the tissue is unknown after the time of injection. Therefore, the effect that the drug or stimuli is having on the tissue during the change is not known since any assay of the response emitted by the tissue during this time cannot be correlated to any definite concentration of the drug or stimuli. The problem of not being able to determine the concentration after injection is further amplified when an injection is made before the concentration in the holding chamber returns back to concentration "x". In this situation, the concentration affecting the tissue at the point in time of the second injection is not known.
In other prior art processes, the concentration affecting the tissue is increased or decreased in a flow through system in a step-like manner. To accomplish a step-like increase or decrease in concentration, the flow of the concentration affecting the tissue is stopped and a second different concentration is introduced into the holding chamber and the concentration in the holding chamber is allowed to equilibrate to the second concentration. The time required to reach equilibrium and the concentration affecting the tissue during this time is not known.
Drugs and stimuli fluctuate in various manners in an intact organism. These prior art processes are not able to emulate these fluctuations and thus cannot provide a physiological environment for the isolated tissue. In addition, it is desirous to selectively manipulate these fluctuations to study the effects of different amplitudes, durations and frequencies of drugs and stimuli.